Alkanediyl bridged benzimidazolo monomethine cyanine dyes, processes for their preparation, and photographic emulsions and elements containing such dyes

ABSTRACT

Alkanediyl bridged benzimidazolo monomethine cyanine dyes are disclosed wherein at least one benzimidazolo nucleus is provided with an electron-withdrawing group. A disclosed preparation of the dyes includes producing an electron-withdrawing group substituted bis(2-nitrophenyl)-2-R 1  -propanediamide, where R 1  is hydrogen or alkyl; converting the nitro groups to primary amine substituents; removing the elements of water to effect ring closure; and thereafter providing the --CR 1  -- linked benzimidazole nuclei so formed with an N,N 1  -alkanediyl bridging group and quaternizing substituents. Dye synthesis is completed by reducing the --CR 1  -- linking group to the corresponding methine. The dyes are useful as sensitizers in silver halide emulsions and photographic elements.



